Condensate droplet size distribution on lubricant-infused surfaces. (June 2017)

• Record Type: Journal Article
• Authors: Weisensee, Patricia B.; Wang, Yunbo; Qian, Hongliang; Schultz, Daniel; King, William P.; Miljkovic, Nenad
• Is Part Of: International journal of heat and mass transfer. Volume 109(2017)
• Page Start: 187
• Page End: 199
• Publication Date: 2017-06
• Subjects: Dropwise condensation -- Dropsize distribution -- Sweeping -- Heat transfer -- Lubricant infused surface (LIS) -- Slippery liquid infused porous surface (SLIPS); Heat -- Transmission -- Periodicals; Mass transfer -- Periodicals; Chaleur -- Transmission -- Périodiques; Transfert de masse -- Périodiques; Electronic journals; 621.4022
• DOI: 10.1016/j.ijheatmasstransfer.2017.01.119
• Languages: English
• ISSNs: 0017-9310

Abstract

Graphical abstract: Highlights: The average distribution of droplet sizes is independent of lubricant viscosity. Droplet sizes at onset of droplet sliding are almost twice as large as predicted. Sweeping rates do not influence the steady-state distribution of droplet sizes. Heat transfer rates are nearly constant along large vertical plates. Heat transfer rates can be 10–15 times higher than for filmwise condensation. Abstract: Condensation is a ubiquitous phenomenon in nature and industry. Heat transfer rates during dropwise condensation on non-wetting substrates can be 6-8X higher than heat transfer rates during traditional filmwise condensation on wetting substrates. Dropwise condensation on lubricant-infused surfaces (LIS, or SLIPS) is particularly interesting due to high droplet mobility on these surfaces. To accurately predict heat transfer rates during dropwise condensation, the distribution of droplet sizes must be known. Here we present condensation studies of water on aluminum-based lubricant-infused surfaces with a wide range of lubricant viscosities (12–2717 cSt) to determine droplet size distributions. Through optical imaging and microscopy, we show that the distribution of droplet sizes on LIS is independent of lubricant viscosity, and agrees well with the model developed by Rose for the distribution of droplet sizes on hydrophobic surfaces, especially in the range 10 < r < 100 µm. Using artificial sweeping experiments and numerical modeling, we investigate the dependence of sweeping rates on the distribution of droplet sizes and on average heat transfer rates. The maximum size to which droplets grow before being swept decreases rapidly with only a modest decrease in sweeping period, from 750 to 62 µm. Yet, the distribution of droplet sizes and heat transfer rates are nearly unaffected by the change in sweeping period, due to a relative insensitivity of heat transfer to droplets with radii r > 100 µm due to a high conduction resistance within these droplets. Our work provides an experimental and analytical framework to predict heat transfer and sweeping rates for water condensation on a vertical plate coated with a LIS or SLIPS surface.